Flexor or extensor tendons are attached to phalangeal bones at very specific and well-localized insertion sites. The only other attachments are filamentous vincular strands. As a result of this physiological structure, transected or torn flexor or extensor tendons are prone to retract proximally within their sheaths. This tendency makes the task of tendon retrieval a difficult one often leading to tendon sheath and pulley system injury.
More specifically as an example, the flexor tendon and its delicate fibro-osseous canal depend on the preservation of smooth continuous surfaces for optimal tendon excursion during joint flexion. One consequence attending sheath disruption during tendon repair is the formation of adhesions between tendon and sheath and resulting damage to the pulley system which ultimately limits flexion or bending of the involved finger.
Doyle and Blythe describe the series of cruciate and annular pulleys that provide the mechanical advantage for optimal flexion at the interphalangeal joints (see Doyle, J. R. and Blythe, W. F. Anatomy Of The Flexor Tendon Sheath And The Pulleys Of The Thumb. J. Hand Surge 2:2; 149-151, 1977). The most important of these are the A2 and A4 pulleys that are responsible for holding the tendons against the shafts of the proximal and middle phalangeal bones. This structural arrangement keeps the moment arm about the PIP joint to a minimum and allows the maximal flexion at the PIP joint for a given tendon excursion distance. The cruciate pulleys are less important in the mechanical aspects of tendon function. Injury to them, however, may create adhesions between tendon and sheath that can be even more crippling than damage to the more important annular pulley structures.
Further, it should be appreciated that nutrients are known to travel to tendons via three routes: the synovial fluid around the tendon, the intrinsic vessels within the peritenon and via the long and short vincular mesenteries. Preservation of these routes requires minimal further disruption of these structures during tendon repair.
Tendon injuries for which it is most difficult to obtain satisfactory functional results are those occurring in zone 2 as described by Verdan. Zone 2 extends from the proximal end of the fibro-osseous flexor tendon sheath to the insertion of the flexor digitorum superficialis tendon at the midportion of the middle phalanx. These are the injuries that often result in the retraction of the tendon within the sheath, thereby setting the stage for lengthy dissections and further injury to facilitate tendon retrieval and repair.
A common method for tendon retrieval is flexion of the finger or digit to shorten the length of the fibro-osseous canal. In certain limited instances this procedure exposes the edge of the tendon so as to allow it to be grasped. Another technique is the blind passage of a hemostat or other clamp within the tendon sheath to grasp the tendon edge. If the tendon cannot be retrieved after three blind passes, most authorities agree that the safest and most efficacious next step is to dissect out the tendon sheath. It should be appreciated, of course, that the unsuccessful blind passes only further traumatize the sheath and possibly the tendon. The subsequent dissection causes still further trauma.
Another method used by many experienced hand surgeons involves the making of a counter incision proximal to the site of injury, usually in the palm, to identify the involved tendon. That tendon is then attached to a guide catheter and passed distally through the tendon sheath where repair is completed.
While the above-described state of the art techniques usually provide access to the tendon for purposes of repair each, unfortunately, further traumatizes the tendon, risks injury to digital vessels and nerves from incisions and causes injury to soft tissue with loss of normal flaps. A need is therefore identified for an improved approach for repairing transected or torn flexor or extensor tendons of the fingers.